Witness: Katrina The haunting National Geographic Channel documentary, constructed largely from home videos, reruns. The network is carried locally on Cox Communications channel 106, which is not on the basic-cable tier, so friend-up if your dial doesn’t go that high. But be warned (again): Sequences leading up to landfall may be the most troubling, in that they document places (including Gulf Coast towns well beyond New Orleans) and people that the storm and levee failures would change forever. Today (August 30), 4 p.m. National Geographic